Browsing by Author "Kono, Kimitoshi"

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An incompressible state of a photo-excited electron gas
(2015-05-01)
Chepelianskii, Alexei D.
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Watanabe, Masamitsu
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Nasyedkin, Kostyantyn
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Kono, Kimitoshi
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Konstantinov, Denis
Two-dimensional electrons in a magnetic field can form new states of matter characterized by topological properties and strong electronic correlations as displayed in the integer and fractional quantum Hall states. In these states, the electron liquid displays several spectacular characteristics, which manifest themselves in transport experiments with the quantization of the Hall resistance and a vanishing longitudinal conductivity or in thermodynamic equilibrium when the electron fluid becomes incompressible. Several experiments have reported that dissipationless transport can be achieved even at weak, non-quantizing magnetic fields when the electrons absorb photons at specific energies related to their cyclotron frequency. Here we perform compressibility measurements on electrons on liquid helium demonstrating the formation of an incompressible electronic state under these resonant excitation conditions. This new state provides a striking example of irradiation-induced self-organization in a quantum system.
Bistable transport properties of a quasi-one-dimensional Wigner solid on liquid helium under continuous driving
(2017-11-27)
Rees, David G.
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Yeh, Sheng-Shiuan
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Lee, Ban-Chen
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Kono, Kimitoshi
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Lin, Juhn-Jong
We investigate low-frequency fluctuations in the transport characteristics of a quasi-1D Wigner solid (WS) moving along a liquid helium substrate in response to a sinusoidal driving voltage. The fluctuations occur between distinct transport modes in which the decoupling of the WS from ripplonic polarons (or "dimple lattice," DL) formed on the helium surface does, or does not, occur during each ac cycle. We demonstrate that a Gaussian-like distribution in the decoupling threshold force gives rise to this bistability, as the low-frequency switching occurs when the probability of decoupling during each ac cycle is small but finite. We attribute the distribution in the decoupling threshold force to the range of structural configurations allowed for the quasi-1D electron lattice, which influences the strength of the WS-DL coupling. Hence, the switching rate between the ac transport modes is extremely sensitive to the microscopic properties of the electron solid.
Can Warmer than Room Temperature Electrons Levitate Above a Liquid Helium Surface?
(2019-05-01)
Chepelianskii, A. D.
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Watanabe, Masamitsu
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Kono, Kimitoshi
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國際半導體學院
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International College of Semiconductor Technology
We address the problem of overheating of electrons trapped on the liquid helium surface by cyclotron resonance excitation. Previous experiments suggest that electrons can be heated to temperatures up to 1000 K, more than three orders of magnitude higher than the temperature of the helium bath in the sub-Kelvin range. In this work we attempt to discriminate between a redistribution of thermal origin and other out-of-equilibrium mechanisms that would not require so high temperatures like resonant photo-galvanic effects or negative mobilities. We argue that for a heating scenario the direction of the electron flow under cyclotron resonance can be controlled by the shape of the initial electron density profile, with a dependence that can be modeled accurately within the Poisson-Boltzmann theory framework. This provides an self-consistency check to probe whether the redistribution is indeed consistent with a thermal origin. We find that while our experimental results are consistent with the Poisson-Boltzmann theoretical dependence, some deviations suggest that other physical mechanisms can also provide a measurable contribution. Analyzing our results with the heating model we find that the electron temperatures increase with electron density under the same microwave irradiation conditions. This unexpected density dependence calls for a microscopic treatment of the energy relaxation of overheated electrons.
Dynamical decoupling and recoupling of the Wigner solid to a liquid helium substrate
(2020-08-24)
Rees, David G.
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Yeh, Sheng-Shiuan
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Lee, Ban-Chen
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Schnyder, Simon K.
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Williams, Francis I. B.
We investigate the dynamical interaction between an electron crystal trapped above the surface of liquid helium and surface waves ('ripplons') excited by its motion. At rest, the electron system is 'dressed' by static ripplons to form 'ripplopolaron' states. As the electrons move, resonant ripplon scattering results in a growth of the ripplopolaron effective mass, on timescales comparable with the inverse of the ripplon frequency (similar to 100 ns). Under sufficient driving force, the electron system decouples from the surface waves and moves at high velocity, before decelerating sharply when the electron solid and surface excitations recouple to form a 'new' ripplopolaron system. The mass of the newly formed ripplopolarons is similar to that in the initial static case.
Dynamics of Fine Particles Due to Quantized Vortices on the Surface of Superfluid He-4
(2019-07-01)
Inui, Sosuke
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Tsubota, Makoto
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Moroshkin, Peter
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Leiderer, Paul
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Kono, Kimitoshi
We have conducted calculations of the coupled dynamics of quantized vortices and fine metallic particles trapped at a free surface of superfluid 4He. The computational result so far indicates that a particle-vortex complex may produce quasi-periodic motions along the surface and that the motions can be enhanced if the metallic particles are heated and induce local radial flows. Our results qualitatively reproduce recent experimental observations of trapped particle motion.
Level Broadening Effect in Electron Tunneling through Double Quantum Dots with Different g Factors
(2011-04-01)
Huang, Shiu-Ming
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Tokura, Yasuhiro
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Akimoto, Hikota
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Kono, Kimitoshi
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Lin, Juhn-Jong
The spin bottleneck effect was first observed in vertical double quantum dots with different g factors in high magnetic fields. We further investigate the spin-dependent resonance tunneling through the same quantum dot system in low magnetic fields. There are no resonance tunneling peak lines, even though one of the Zeeman levels is aligned, because the mismatch of the other Zeeman sublevels blocks the resonance tunneling. However, the level broadening effect partially releases the spin-dependent blockade. As a compromise between two effects, one resonance tunneling peak line splits into two peak lines and forms a kink structure. The split of the two current peak lines is half of Zeeman energy difference between two dots. (C) 2011 The Japan Society of Applied Physics
Melting of Wigner Crystal on Helium in Quasi-One-Dimensional Geometry
(2015-05-01)
Ikegami, Hiroki
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Akimoto, Hikota
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Kono, Kimitoshi
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物理研究所
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Institute of Physics
We discuss melting of a Wigner crystal formed on a free surface of superfluid He, in quasi-one-dimensional (Q1D) channels of width between 5 and 15 m. We reexamine our previous transport data (Ikegami et al. in Phys Rev B 82:201104(R), 2010), in particular, by estimating the number of electrons across the channel in a more accurate way with the aid of numerical calculations of distributions of the electrons in the channels. The results of reexamination indicate more convincingly that the melting of the Wigner crystal in the Q1D geometry is understood by the finite size effect on the Kosterlitz-Thouless-Halperin-Nelson-Young melting process. We also present technical details of the transport measurements of the electrons in a Q1D geometry, including a fabrication method of devices used for the transport measurements, numerical simulations of response of the devices, and a procedure for analyzing transport data.
Observation of Intrinsic Magnus Force and Direct Detection of Chirality in Superfluid He-3-A
(2015-04-15)
Ikegami, Hiroki
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Tsutsumi, Yasumasa
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Kono, Kimitoshi
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物理研究所
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Institute of Physics
We report details of the observation of the intrinsic Magnus (IM) force acting on negative and positive ions trapped just below a free surface of the A phase of superfluid He-3 (He-3-A). From the transport measurements of the ions along the surface, we found that the IM force acts on both the negative and positive ions. We also demonstrate that the transport measurements could distinguish whether the surface is composed of a chiral monodomain or multiple chiral domains. For multiple chiral domains, the current of the ions was found to be irreproducible and unstable, which was reasonably explained by the formation of the chiral domain structure and the dynamics of the chiral domain walls. For chiral monodomains, the appearance ratio of chirality emerging upon cooling through the superfluid transition temperature was found to depend on the direction of the external magnetic field, which implies the existence of an unknown coupling between the chirality and the magnetic field.
Reentrant Melting of a Classical Quasi-One-Dimensional Wigner Crystal on the Surface of Liquid Helium
(2013-12-01)
Rees, David G.
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Ikegami, Hiroki
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Kono, Kimitoshi
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物理研究所
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Institute of Physics
We present transport measurements of electrons on the surface of liquid helium confined to a microscopic channel, the effective width of which can be controlled electrostatically. Above 1 K the electron system is liquid-like and the conductance varies smoothly with the channel width. At lower temperatures the system forms a classical quasi-one-dimensional Wigner crystal ( WC). Close to the WC melting temperature, the current oscillates as the channel width is varied, due to reentrant melting as recently reported [H. Ikegami, H. Akimoto, D. G. Rees, and K. Kono: Phys. Rev. Lett. 109 ( 2012) 236802]. In the WC regime we observe Bragg-Cherenkov ripplon scattering, a signature of strong spatial electron order, for both the widely open channel and the single electron chain.
Review: Observation of Majorana Bound States at a Free Surface of <mml:msup>3</mml:msup>He-B
(2019-05-01)
Ikegami, Hiroki
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Kono, Kimitoshi
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電子物理學系
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Department of Electrophysics
The p-wave superfluid 3He is a textbook example of topological superfluids. Among its multiple superfluid phases, the B phase (3He-B) is known as a topological state protected by time-reversal symmetry. One of the important topological features of 3He-B is the formation of bound states at its surface. Notably, such surface Andreev bound states are predicted to be Majorana fermions, i.e., their antiparticles are identical to their particles. Because of the well-elucidated bulk properties of the superfluid 3He owing to its cleanliness, 3He-B provides an ideal platform to pursue Majorana fermions in condensed matter systems. In this article, we review recent investigations of surface Andreev bound states by the mobility of ions trapped below a free surface of 3He-B. The free surface is an ideal surface providing a specular boundary condition; the surface Andreev bound states formed there are expected to be Majorana fermions with a well-defined energy spectrum. We show that the temperature and depth dependences of the experimentally obtained mobility of negative ions (Ikegami et al. in J Phys Soc Jpn 82:124607, 2013) are quantitatively reproduced by a theoretical study that includes scattering of the surface Andreev bound states (Tsutsumi in Phys Rev Lett 118:145301, 2017). This quantitative agreement unambiguously demonstrates the experimental detection of surface Andreev bound states. We also discuss the future prospects of the Majorana physics in He-3-B.
Spin transport from doublet state to triplet state in vertical quantum dots
(2008-04-01)
Huang, Shiu-Ming
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Akimoto, Hikota
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Kono, Kimitoshi
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Lin, Juhn-Jong
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Tarucha, Seigo
We measured electron transport state spectra of an In(0.05)Ga(0.95)As vertical double quantum dot. Both the ground and excited states of transport spectra from two electrons to three electrons are measured using a large source-drain voltage. In the obtained transition spectrum, the ground state transition from the 1S(2) singlet state to the 1S2P triplet state is observed at 5 T. Zeeman splitting with a g-factor of 0.36 is clearly observed at magnetic fields higher than 5 T. The observation of two Zeeman sublevels instead of three for the triplet state is explained by the spin selection rules for the S(Z) components between the two-electron and three-electron spin states. Transition with the total spin difference between the initial and final states larger than 1/2 is forbidden. Because the transition between doublet states is much longer than electron tunneling, both spin up and spin down can be the initial states from spin transitions. There are four transitions contributing to tunneling processes, but only two energy differences lead to the two Zeeman sublevels in the excitation spectra.
Stick-Slip Motion of the Wigner Solid on Liquid Helium
(2016-05-16)
Rees, David G.
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Beysengulov, Niyaz R.
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Lin, Juhn-Jong
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Kono, Kimitoshi
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電子物理學系
We present time-resolved transport measurements of a Wigner solid (WS) on the surface of liquid helium confined in a micron-scale channel. At rest, the WS is "dressed" by a cloud of quantized capillary waves (ripplons). Under a driving force, we find that repeated WS-ripplon decoupling leads to stick-slip current oscillations, the frequency of which can be tuned by adjusting the temperature, pressing electric field, or electron density. The WS on liquid He is a promising system for the study of polaronlike decoupling dynamics.
Structural order and melting of a quasi-one-dimensional electron system
(2016-07-29)
Rees, David G.
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Beysengulov, Niyaz R.
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Teranishi, Yoshiaki
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Tsao, Chun-Shuo
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Yeh, Sheng-Shiuan
We investigate the influence of confinement on the positional order of a quasi-1D electron system trapped on the surface of liquid helium. We find evidence that the melting of the Wigner solid (WS) depends on the confinement strength, as well as electron density and temperature. A reentrant solid-liquid-solid transition is observed for increasing electron density under constant electrostatic confinement. As the electron row number N-y changes, varying commensurability results in a modulation of the WS order, even when N-y is large (several tens). This is confirmed by Monte Carlo simulations.